Networked devices (e.g., a layer 2 switch) that support certain IEEE standards and quality of service prioritization schemes may receive and process Ethernet frames that include virtual local area network (VLAN) tagging. Typically, a VLAN tag in an Ethernet frame header includes a 3-bit field that defines priority. The switch may use the value of these priority bits to differentiate incoming traffic. The switch often handles different types of incoming frames, such as unicast, multicast, broadcast, and flood frames. Unicast frames are frames that are sent from a single source and are intended for a single destination in a network. In comparison, broadcast and multicast frames are generally intended for multiple destinations in a network. Flood frames are frames for which no destination is found and therefore are broadcasted to all destinations. Typically, when a switch receives an incoming frame that is VLAN-tagged, the switch forwards the frame to a buffer pool for further processing (e.g., for replication in the case of broadcast or multicast frames). The buffer pools may be separated by traffic class. Unicast frames typically require less processing than broadcast or multicast frames.
Typically, a switch determines a traffic class for a given frame based solely on priority bits identified in the VLAN tag. Consequently, unicast frames, which require less processing than multicast frames or broadcast frames, may be assigned to similar traffic classes as multicast or broadcast frames, which require more processing than unicast frames. That is, this approach determines a traffic class independently from the type of frame. Compared to unicast frames, processing multicast or broadcast frames may be more computationally expensive. For example, assume that frames with a priority bit value of 1 are assigned to traffic class 5. If the switch receives relatively few incoming multicast frames, then unicast frames may flow easily through the switch. However, if the switch receives considerably more incoming multicast frames, the unicast frames may take longer time to flow through the switch.